When Sifrhippus sandae, the earliest known horse, first appeared in the forests of North America more than 50 million years ago, it would not have been mistaken for a Clydesdale.

It weighed in at around 12 pounds--and it was destined to get much smaller over the ensuing millennia.

Sifrhippus lived during the Paleocene-Eocene Thermal Maximum (PETM), a 175,000-year interval of time some 56 million years ago in which average global temperatures rose by about 10 degrees Fahrenheit.

The change was caused by the release of vast amounts of carbon into the atmosphere and oceans.

About a third of mammal species responded with a significant reduction in size during the PETM, some by as much as one-half.

Sifrhippus shrank by about 30 percent, to the size of a small house cat--about 8.5 pounds--in the PETM's first 130,000 years, then rebounded to about 15 pounds in the final 45,000 years of the PETM.

Scientists have assumed that rising temperatures or high concentrations of carbon dioxide primarily caused the "dwarfing" phenomenon in mammals during this period.

New research led by Ross Secord of the University of Nebraska-Lincoln and Jonathan Bloch of the Florida Museum of Natural History at the University of Florida offers evidence of the cause-and-effect relationship between temperature and body size.

Their findings also provide clues to what might happen to animals in the near future from global warming.

Teeth of Sifrhippus at its larger size with teeth from the same species after its size shrank.

Animals tend to be larger in colder climates. Surface area is proportional to the square of linear dimension, whereas mass and volume are proportional to the cube. In a cold climate you want a low surface-to-mass ratio to minimize loss of body heat, whereas in a warm climate you want just the opposite.

to Buddha 12 - the Earth many millions years was in System of planets of other Galaxy, the base civilization of this planet could create kinds of plants and insects, kinds of animals lived on land and at ocean - the various sizes and the form, homo sapiens on this planet provided functioning Эcо of the conveyor in planetary scale. The Dynamic model of the globe has proved, why changes which have taken place (after occurrence of the Earth in Solar system) there were fatal to a base civilization, and also for many kinds mega faunae and mega florae

to Buddha 12 - and in general on this planet the climate never globally varied (after occurrence in Solar system), and (repeatedly) position of an environment of a planet in limits (25 о) globally varied, this fact do not take into account authors which compose absurdity about events in the past

to Buddha 12 - the Earth many millions years was in System of planets of other Galaxy, the base civilization of this planet could create kinds of plants and insects, kinds of animals lived on land and at ocean - the various sizes and the form, homo sapiens on this planet provided functioning Эcо of the conveyor in planetary scale. The Dynamic model of the globe has proved, why changes which have taken place (after occurrence of the Earth in Solar system) there were fatal to a base civilization, and also for many kinds mega faunae and mega florae